A phosphoprotein found in dentin is bound to collagen fibrils at a site coincident to that where mineralization of the tissue takes place. About 37% of the amino acid residues of the protein are phosphoserine and 33% are aspartate. The ability of this phosphoprotein to bind calcium will be studied by determining the calcium-binding constant. The selectivity of binding will be ascertained by determination of the affinity for calcium in the presence of competing cations. The effect of calcium upon the conformation of the phosphoprotein will be ascertained by obtaining CD spectra of the protein in the presence of incremental levels of calcium. And finally, since the binding of the phosphoprotein to collagen may be an important event in the mineralization process in dentin, the ability of the phosphoprotein to bind the soluble and insoluble collagens will be determined.